Automotive Air Conditioning Information Forum

Hi All

I have been trying to troubleshoot an issue i am having with my Ford AU Fairlane (its and Australian car based off the Lincoln Design)
Basically when i am running the car particularly on days over 29 degree C (84F) after about 10 min I can feel the air get warm in the vent, Then it will go cold again. then warm and then cold. when i stop the car and check the the temperature of the pipe and see if it is showing signs of operation i am finding the compressor is not running and the pipe up stream of the orifice tube is warm.

The Compressor will usually kick in again then and it will start blowing cold intermittently again.

I can not reproduce this when i have it in the carport with the gauges connected. when they are connected i am getting the low side pressure of about 20psi and high side 250psi (with thermos fans on low speed) when the engine is at 2000rpm and between 30 and 40psi with high side 280psi with thermos fans on low.

When the thermos fans run on high the high side will drop to around 200psi at 2000rpm.

The thermos fans dont seem to come on very much at all.

Where should i start to troubleshoot this issue? it seems that i need to take it on the highway for a fair length of time to actually test it so it is really difficult to actually see what the system is doing when the fault is happening.

A few questions: What year is your car, what engine does it have, and has the system ever been serviced?

The car is a 2000 model, the engine is a 5L V8 engine, and to my knowledge it has not been serviced however i am a second owner of the car so i can not confirm.

Similar symptoms to my 1998 Frontier AC about 1.5 years ago. I had soldered on a wire to the compressor wire on mine, which I routed to a blue indicator light on the dashboard. So I noticed that when my cooling stopped that the compressor was still getting positive voltage. So when the air went warm, I pulled over immediately, and saw that the compressor (center part, drive plate) was NOT turning, just the outer pulley was, so I knew that the AC clutch was slipping.

I was fortunate on mine, all I had to do on mine to reduce the "AC clutch gap" was to remove a thin shim under the drive plate; this is a legitimate repair too, not a backyard fix.

So I say to check for clutch slippage visually, as soon as the air starts coming in warmer.

On yours: a completely unrelated reason from above could be an actuator allowing in heat, like opening a blend door in the dash.

Also a question for yours: is the VOLUME of air staying the same when this happens???

Cusser wrote:...reduce the "AC clutch gap"...remove a thin shim under the drive plate... .
...So I say to check for clutch slippage visually, as soon as the air starts coming in warmer.
...On yours: a completely unrelated reason from above could be an actuator allowing in heat, like opening a blend door in the dash.
Also a question for yours: is the VOLUME of air staying the same when this happens???

Great suggestions and question. I would add: Since we don't know the vehicle's history, let's also ensure that the charge is correct by recovering what's in it now, then evacuating and recharging to spec. I don't have A/C system specifications for Australia vehicles, but hopefully the under-hood decal with that information is still there.

I have noticed when this does happen the compressor does appear to have stopped so perhaps i could try that with the indicator light even if it is just a temporary addition to see what is going on.

According to the Charge specs the on the front of the car the charge is listed as 850g +-50g
The refrigerant is fairly heavily regulated to protect the industry over here so is a little hard to buy outright (its not possible to buy it over the counter in Australia as refrigerant however they do sell a product called "freeze spray" that is just 100% 1 1 1 2 Tetrafluroethane) the bottles are 250g so it would take 3.5 cans of it to charge from empty. I would probably like to add some uv die to the system too in order to detect future leaks.

The volume of air coming out at the vents is the same when this happens you just notice the air becomes warm.
I could probably test the blend door issue by removing the vacuume line from the heater tap.

I doubt refrigerant level would cause cycling between hot and cold unless the level was so low that it stopped the compressor engagement due to low pressures.

Make sure the fan clutch or electric fans in the engine compartment are all working properly, especially if cooling is better on the highway than in traffic/idle.

bazzybtec wrote:I have noticed when this does happen the compressor does appear to have stopped so perhaps i could try that with the indicator light even if it is just a temporary addition to see what is going on.

Great idea as said before.

bazzybtec wrote:According to the Charge specs the on the front of the car the charge is listed as 850g +-50g

Sounds correct. Glad the decal is still there.

bazzybtec wrote:The refrigerant is fairly heavily regulated to protect the industry over here so is a little hard to buy outright (its not possible to buy it over the counter in Australia as refrigerant however they do sell a product called "freeze spray" that is just 100% 1 1 1 2 Tetrafluroethane) the bottles are 250g so it would take 3.5 cans of it to charge from empty. I would probably like to add some uv die to the system too in order to detect future leaks.

I figured that Australia would be tough on non-professionals when it comes to refrigerants. Be sure to read the label carefully on the "freeze spray," though. You don't want anything besides pure R-134a in your A/C system. The addition of a little UV dye is fine.

Your vehicle is about 20 years old, and we're unaware of its service history. You might have a condensing problem, but you could also have a refrigerant charge that's off, as well as air and moisture in the system. We just don't know. So I'd begin with recovery, a thorough evacuation, and weighing-in the correct charge using a precise refrigerant scale (or have it done by a competent mobile A/C shop) before additional testing and diagnosis. Changing the desiccant while the system is open is also a good idea.

HI
would be most likely a debris blocked evaporator causing freezing of the core. Be the first job I would do. Sometimes the vent airflow can be reduced but only only occasionally noticeable .
Clamp heater hose is also a cheap way of diagnosis .
Does the low side reading go low and if so how low jut b4 cutting out . The over temp sensor can be bypassed to check .

bazzybtec wrote:I have noticed when this does happen the compressor does appear to have stopped so perhaps i could try that with the indicator light even if it is just a temporary addition to see what is going on.

Yes, would be of GREAT value to know if the AC clutch is getting voltage when the drive plate (center) stops turning.